1. Field of the Invention
This invention relates to electroplating of chromium, and, more particularly, it is concerned with an improved process of forming an adherent chromium electrodeposit on a chromium substrate.
2. Description of the Prior Art
Normally, electrodeposited chromium does not adhere well to a chromium underlayer, and for this reason electrolysis must not be interrupted during the plating process. If the article needs to be removed from the solution for any reason, the plating process must be restarted in a special way. Fink, in U.S. Pat. No. 1,942,356, describes the only known method of obtaining an adherent chromium electrodeposit on such a chromium substrate. The method disclosed by Fink comprises warming the chromium part to the bath temperature and then applying voltage slowly until the plating current is reached. Subsequently, Weiner and Walmsley included a mild anodic electrochemical etching step in the Fink process, as described in Chromium Plating, Finishing Publications Ltd., Teddington, England (1980) p. 147-8.
The Fink process works well for the conventional sulfate, or a mixed catalyst chromium electroplating bath, and for the 25% efficiency bath described by Chessin and Newby in U.S. No. 4,588,481.
Unfortunately, however, it is not satisfactory for the high energy efficiency (HEEF) baths such as described by Chessin in U.S. Pat. No. 4,472,249, where the efficiency is 40% or higher.
Accordingly, an object of the present invention is to provide an improved process of electro-depositing adherent chromium onto a chromium substrate.
Another object herein is to provide such a process which can be used with the HEEF-40% efficiency chromium baths.
Still another object is to provide a method which can be applied after an interruption in the plating chromium process.